1. Field of the Invention
The present invention relates to an electronic apparatus, a fan unit, and a subrack, and more specifically, to an electronic apparatus with a cooling structure particularly suitable for a radio base station apparatus, a fan unit, and a subrack suitable for cooling the electronic apparatus.
2. Description of the Related Art
A cooling structure for cooling an electronic apparatus by using an axial fan is disclosed, for example, in Japanese Patent Laid-Open Publication JP 2000-59061 A and JP 2002-118387 A. JP 2000-59061 A discloses an electronic apparatus equipped with a casing, and a plurality of electronic component modules accommodated in the casing. Here, a fan in the electronic apparatus sucks the air within the casing to generate an airflow inside the casing, and the sucked air is discharged through an exhaust port. JP 2002-118387 A discloses a computer cooling structure. Here, in a computer equipped with a cooling axial fan for dissipating heat generated in an electronic component module into the atmosphere, exhaust ports are formed in two side surfaces of the casing. Such a cooling structure using an axial fan is also applied to conventional radio base station apparatuses.
A conventional radio base station apparatus contains, inside an apparatus frame having an open-rack structure, a subrack for accommodating a large number of electronic component modules. Nowadays, regarding radio base station apparatuses, since packaging density, in particular, is becoming increasingly higher, it is important to efficiently dissipate the heat generated from the large number of electronic components. An example of a conventional radio base station apparatus cooling structure will be described with reference to FIGS. 1A through 2B.
FIGS. 1A, 1B, and 1C are a front view, a side view, and a plan view, respectively, schematically showing the construction of a conventional radio base station apparatus. FIG. 1B shows a cooling air 220a and a cooling air 220b generated by a cooling fan described below.
The radio base station apparatus is equipped with an apparatus frame 200, electronic component module groups 211a through 211c, subracks 210a through 210c, and fan units 212a and 212b. Within the apparatus frame 200, a plurality of subracks 210a through 210c are stacked in the height direction. The subracks 210a through 210c accommodate the electronic component module groups 211a through 211c each composed of a large number of electronic component modules. Within the apparatus frame 200, there are further arranged the cooling fan units 212a and 212b for cooling the electronic component module groups 211a through 211c. In the example shown in FIG. 1A, one fan unit 212a is provided above the uppermost subrack 210a. Further, the fan unit 212b is provided above the middle subrack 210b. 
In FIG. 1A, the fan unit 212b is used for the purpose of cooling the middle and lowermost subracks 210b and 210c. Although not shown, the fan units 212a and 212b of FIGS. 1A and 1B have axial fans. When axial fans are used, cooling air thereby generated flows in the direction of the rotation axes of the fans, and is discharged upwardly as shown in FIG. 1B. The direction of the cooling air has a great influence on the arrangement of the subracks and, at the same time, imparts dimensional limitations to the fan units.
That is, as shown in FIG. 1B, it is necessary to provide, in addition to the fan unit 212b, a duct 230 with a partition 231 between the middle subrack 210b and the uppermost subrack 210a. The duct 230 forms a flow passage for causing the cooling air 220b to head for the rear side. Further, the partition 231 forms a flow passage for preventing interference with each other of the exhaust air of the middle-stage fan unit 212b and the intake air of the upper-stage fan unit 212a, which are generated as a result of the adoption of the axial fans. The cooling air 220a from the upper-stage fan unit 212a is discharged through a top portion of the apparatus frame 200 having an open-rack structure. The cooling air 220b intercepted by the partition 231 in the duct 230 is discharged toward the rear side of the apparatus frame 200. In this conventional radio base station apparatus, the duct 230 between the subracks 210a and 210b constitutes a factor leading to rather low accommodation efficiency for the subracks in the apparatus frame 200.
Apart from this, there exists a known example which adopts, in the fan unit for cooling the subrack, a radial fan (a fan exhausting air in the radial direction) requiring no such duct 230 as described above. When adopting a radial fan, one fan unit usually accommodates one radial fan in order to avoid interference of exhaust airflows. However, in the case of a thin-type radial fan, there is involved a shortage of cooling capacity with a single radial fan. Thus, in a subrack for an electronic apparatus of large heat generation amount, the arrangement of a fan unit with a plurality of radial fans is indispensable. In arranging a plurality of radial fans, interference of exhaust airflows from the radial fans must be taken into consideration. FIG. 2A is a front perspective view schematically showing a construction of a subrack 210d accommodating a fan unit 240 in which a plurality of radial fans are arranged. FIG. 2B is a sectional view taken along the line I-I′ of FIG. 2A. As shown in FIG. 2B, generally speaking, a plurality of radial fans 241 are arranged two-dimensionally in a row inside the fan unit 240. Although not shown, an opening is provided in the bottom surface of the fan unit 240. A plurality of electronic component modules is arranged under the fan unit 240. Further, exhaust ports 242 are provided on the rear side of the fan unit 240. A cooling air 243 is discharged through the exhaust ports 242. JP 2000-59061 A, mentioned above, includes a statement to the effect that the adoption of radial fans is also possible.
Here, to secure the requisite cooling capacity, it is necessary to provide additional radial fans. However, JP 2000-59061 A and the example shown in FIGS. 2A and 2B only teach the installment of a single row of radial fans; with a single row of radial fans, there is a fear of the requisite cooling capacity not being secured. Further, even if, in the fan unit of FIGS. 2A and 2B, additional radial fans are provided on the front side of the subrack, the cooling air from the additional radial fans provided on the front side is not discharged since the exhaust ports are only provided on the rear side of the subrack. As a result, a deterioration in cooling capacity is involved.
As stated above, the accommodation efficiency of a subrack accommodated in a radio base station apparatus greatly depends on the cooling structure thereof. However, it has been rather difficult to obtain a radio base station apparatus capable of enhancing the accommodation efficiency of the subrack and securing the requisite cooling capacity.